The degree to which ultrasound imaging can accurately describe atherosclerotic plaque components is currently not well understood. Previous work has shown that there are differences in sound absorption and reflection by different tissue components in these lesions. The idea that echogenic features can be used to describe morphologic changes appears to be reasonable. Since current concepts of stroke and of lesser degrees of cerebral ischemia focus on the role of hemorrhage into plaques, ulceration and plaque excavation, and mural thrombus, the ability to demonstrate such events in patients and to follow progression and regression of the lesions are obviously of paramount importance. The proposed study will utilize endarterectomy specimens to obtain precise spatial correlations of ultrasound reflection features of various plaque components with morphologic findings. Computer based signal amplitude processing, as well as quantitative expressions of echo pattern homogeneity will be used to determine specificity and sensitivity of ultrasound in discriminating plaque components. These studies will provide an experimental data base which is deemed essential for accurate interpretation of clinically derived ultrasound images.